Dear WW,
Welcome to this site! It has many wise and compassionate people that are happy to be there for you.
Ahhh the heartbreak and dilema of drugs !
I have sadly had my share of this problem too. My daughter(at the time in her teens) opened a whole new nightmarish world to me. I learned so much about addiction. What it was, and what it does to the addict and those they love.
The difficulties you describe are very typical. (That isn't to say that they aren't awful,or hard to bear, because they are).
People who start using drugs are usually using to ward off some other painful experience/feeling.
It becomes a way of coping ! Sometimes people start off "for fun", "curiosity" etc.,but that is not what keeps them using. If your boyfriend says he is only using occasionally, are you sure? The lies are all part of the drug using profile. They are often ashamed, fearful, in some sort of pain, and want to keep that drug available. So they hide it !! This is part of their sickness. For those that love them, so many things come up. As you mentioned trust goes out the window ! Right? When the trust is gone it makes the relationship so much harder. Love itself is at risk. Could you talk to him and try to explain your concern without judging or condemning him ? Do you think he would speak with a doctor who could direct him to further help ?
Do you think he is ready to deal with and face his problem? In the meantime, you are going to have to make some hard decisions for you. Narcannon support groups can often be very helpful for the family members of those that are using.This is NO reflecton on the fact that your partner is a loving, good man. He just needs some really good help and you need help to deal with your distress in the meantime.
I can tell you it took my daughter some years to staighten out her life, but she did. She is a wonderful, loving, devoted mother to her 9 yr. old son. She was in and out of treatment a few times. She fell down over and over again and I thought that I would go mad at times. But she is at her core a good person, and by the sounds of it, so is your partner, and he can get out of it too. Begging doesn't work. Crying doesn't work.
Leaving works only in extreme cases. Loving does work, but you need help to know the best ways to offer it. I hope I haven't frightened you, but it is a dangerous and pervasive thing. Untreated/unaddressed it will only escalate. They are the biggest victims and the biggest losers. All those who love them can make a world of difference, but they(the user) themselves have to face it and do the work.