My boyfriend doesnt trust me, thinks i am cheating.

That isn't necessarily related to adoption at all, though that could be a root cause. Many people are that way-- codependent. There is nothing you can do. He has to work through it himself in his own time. Could be many years or never. He is probably best paired with a woman with a similar issue. He needs a desperate woman to hang onto him. Over time people like that will really annoy those who don't have such emotional/maturity issues.