My boyfriend is overwhelming me because of trust issues, how can I help him trust me?

It depends. Trust issues likely have to do with his past experiences. Severe trust issues can even be delusional as with delusional jealousy. If you have given him no reason to distrust you then it possible that he could develop trust over time. However, if that is the case then he may need professional help in dealing with his trust issues.
Difficult ? . We can change ourselves , but we can't change others . If. U. Have known each other for a long time. And still he is not trusting u , may ve his paranoid. And he is what he is, but if u have not been with each other for a long time. , than give him time to know u better. Un addition u c oils ask. Him what can I do more for y to trust me?!
Be trustworthy. Being consistently trustworthy is part of integrity. Remember that sometimes lack of trust can be like jealousy when a person may project their own insecurities on their partner. If you are trustworthy, then your boyfriend might have some jealousy issues possibly related to his own self-image. Beware this, it can destroy relationships if not addressed. Behavioral counseling helps.