I really think I only truly love my bf when I'm high.
Are you sure? Why do you only feel that way when you're high?
I feel like I'm less inhibited during those times, I'm not afraid to say the things I would not normally say otherwise.
It's understandable that you feel like you may only love him when you're high and this is a good question to ask if you're planning to make your relationship work! You should try staying sober for a while and see how you feel about him then.
It's just a phase. I'm not sure if it's love though.
It may only be a phase, but how would you feel if your boyfriend only loved you when high and you found out about it? My advice would be to speak with him about it and try working through it.