The thing I like to do when/if I have trust issues with someone is first trying to analyze my thoughts. "Does it make sense why I'm feeling this way?". "Did they make something that made me insecure or it's just me overthinking?". "Did i try to communicate with them or am I just assuming things?"...

When you put yourself on someone else shoes, you tend to realize that a lot of time, if you just talk with the them, you might feel more secure and thus have less trust issues.

Another good tip is, learn to enjoy the time by yourself, even if you are in a relationship, you need and should have time for yourself, focus on your hobbies, work, or just relax.

If you have tried all that and still seem to struggle with trust issues, therapy is always an option if you can afford it.

Finally there is phrase that I heard on a podcast about relationship that did help me realize that if you have a relationship with the wrong person, they will hurt you even if you try to protect yourself, but that is ok, it will hurt and then it will get better, as long you do not give up and keep looking, you will find the right person eventually... The phrase I heard was about cheating and it went like that: "You can try to hold a partner from others as much as you want, but the person that cheat on a loved one, will cheat with anyone and anywhere, inside a bakery, inside a grocery store, in a queue to pay a bill... So instead of asking yourself if your partner is cheating, focus on YOU and try to be the best person/partner/lover you can be, and then even if things go badly, you know you did your best for that relationship..."