First, I just want to say a few things. Rabid introspection can be a dangerous thing, but good ole fashioned examining ourselves is recommended in scripture, 2 Corinthians 13:5, "Examine yourselves to see whether you are in the faith." I bring this up for two reasons, and two reasons only. First, you talked of being worried about going to Hell if you commit suicide because God dislikes it. Suicide is sinful, but our hope is in Jesus Christ, not our own merits. That being said, suicide is a selfish thing that dishonors God. Even so, go to Christ. Whether you are lost or saved, remember what Jesus faulted the Pharisees for, "you refuse to come to me that you may have life.(John 5:40)"
Second, you stated that you had been lusting after this girl for a long time. It sounds like you idolized this girl, but that length is a little concerning. That being said, idols do creep into our lives. Idolizing a particular girl is a dangerous thing for us, and I would have to admit that I have done the same. Even so, God disciplines his children. Hebrews 12:8 "If you do not experience discipline like everyone else, then you are illegitimate children and not true sons." Just make sure, are you devoted to this girl, or Christ? It's an important question to answer, and our souls rest on it.
I'm a dude who has been going through a season of loneliness too. It is super easy to pity ourselves. I have to say, however, that Christ is faithful even when we are lonely. I tell you this because it has been the most remarkable blessing to me recently: Go to Christ. When you are lonely, seek to commune with him. When you are in despair, tell him. I wish I had learned this lesson earlier than I have. Loneliness can be an awful trial, but it is also a gift. In 1 Corinthians 7:7 Paul says about his own singleness, "I wish that all were as I myself am. But each has his own gift from God, one of one kind and one of another." If God is our Father, then singleness isn't a curse. We actually have more time than married people to seek Christ. Psalm 56:8 says, "You have kept count of my tossings; put my tears in your bottle. Are they not in your book?" Go to the one who knows all of your tears.
Just a word to encourage, I found myself in despair because of my loneliness last week. Eventually, I discovered that I had been spending way too much time with others before in my life, and that my busyness had left my relationship with Christ to decay. So, I fasted and sought the Lord. I can't say my prayers were anything special, but I can say that he heard me. It took a few days, but eventually he started pouring out his lovingkindness again. There is a reason that Christ taught in Matthew 7:7, "Ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you.."
Well, I hope something in there helps. Hopefully none of it came off as hypocritical or useless.