God does tell us who to love.
Matthew 22:37-38 says - "Jesus said unto him, Though shalt love the Lord they God with all they heart, and with all they soul, and with all they mind. THIS is the first and great commandment" (emphasis added).
God wants us to love Him first. Above all other people or things. Which means it may be asked of us to give up someone we love because loving them means we won't be putting God first, which means keeping ALL His commandments. Again in Matthew we read, "He that loveth father or mother more than me is not worthy of me: and he that loveth son or daughter more than me is not worthy of me."
In other words, we aren't to love anyone more than God.
In a great talk, The Great Commandment -- Love the Lord, given a number of years ago, President Ezra Taft Benson said, "Can we put God ahead of security, peace, passions, wealth, and the honors of men? When we put God first, all other things fall into their proper place or drop out of our lives. Our love of the Lord will govern the claims for our affection, the demands on our time, the interests we pursue, and the order of our priorities."
Awhile ago I had a conversation with a friend about same gender couples and how it wasn't right that the Church would say that people can't love those they love. I agreed that it was a heart-wrenching thing that seemed very unfair. It is so hard when what you feel and want seems to be denied to you. I understand the questions of why would God ever ask that or do that to someone? I don't why some things are the way they are; the whole why behind who we are attracted to (mostly because I think this is a complicated formula that consists of many factors) and the complicated thing we call love. Ultimately, the gospel doesn't tell us who we can't love but tells us who we should love and who should come first in our love and all our affections. 
People have given up family, wealth, position and even their very lives for this gospel, so though sometimes it definitely isn't fair (I'm sure all those people that gave up those things would say it didn't feel fair) they were willing to do it because loving God should come before anything else and for most of us we will be asked to give up something if we strive to live the gospel with our whole hearts, minds and strengths!The thing is, God doesn't ask us to put Him first and to love Him above all else because He needs an ego boost. God doesn't ask us to love Him for Him - if He did, He wouldn't love all those that don't love Him. He asks us to love Him and put Him first for US.
For a couple years after I turned 18 I was inactive from the Church. Back then, I figured I had been there, and done that for 18 years and that was enough. But one day a couple years after I had stopped going to church, I went to see a movie on my own. I was sitting there before the movie started feeling extremely discouraged about life and feeling like there was no purpose to me being there. A few seats down and older gentleman sat down and he began to talk to me, asking how I was, about my life, sharing things about his life and his wife. He was very kind and showed a genuine interest and concern about me - someone he didn't even know. When the movie started, it had only been about 5 minutes into the movie, he got up and left. He never came back. As the movie was finishing, I started to think about how odd that was - nothing questionable had happened in the movie - not much happens in the first 5 minutes, so I wondered why he had left and why he had come to the movie.
Just then, a thought came to my mind that was very powerful and not my own - it said, "That man was there for you because I want you to know that I know you, am aware of you, and that I love you." That started my journey to gaining my own testimony of the gospel and gave my testimony the foundation that God loved me. In the years since then, I've had numerous experiences and confirmations until I have no doubt in my mind of God's love for me and each of us. That He loves us more than we can even comprehend, and that what He asks is ALWAYS the best for us, even if it doesn't seem or feel that way at the time. Mark 10:29-30 tells us, "And Jesus answered and said, Verily I say unto you, There is no man that hath left house, or brethren, or sisters or father or mother, or wife, or children, or lands, for my sake, and the gospel's, But he shall receive an hundredfold now in this time, houses, and brethren, and sisters, and mothers, and children, and lands, with persecutions; and in the world come eternal life."
As Preach My Gospel says so well, "All that is unfair about this life will be made right through the Atonement of Jesus Christ." I don't how this will be. I don't know how the heartache we've each suffered and the difficulty we faced when we give up people we love, or a life we feel and want can be made right but because I know the Lord loves us more than we comprehend I know it will be. And it will be more glorious and wonderful and worth everything I gave up in this life to strive to follow Him and love Him before anyone or anything in this life.
And He does not leave us alone. He knows when our hearts are breaking because we are trying to put Him first. I know He will succor us and helps us through ANYTHING if we turn to Him and through doing the things He asks us to do - reading our scriptures, prayer, living in a repentant state, attending church, partaking of the sacrament, attending the temple. Each of these things bring the power of the Lord into our life and allow the enabling power of the Atonement to flow through us. It doesn't mean our hearts will be changed (though that is possible) or that who we are attracted to will suddenly change, or our family will accept us and the gospel or that it won't hurt beyond what we ever thought we could withstand. But it does mean the Lord will bless us with the strength to keep moving forward and to feel peace and joy. It will take effort and desire but the help is there.His arms are always outstretched. He loves us and asks us to love Him so we can be changed so one day we can be like Him and live with Him being able to receive all He has.
For me that means, I will take each day as it comes, accepting that some days and things are going to hurt beyond measure but trusting in a love I know more surely than anything else.
