My boyfriend might have been married

Nabella
Hi I'm 23 years old and my BF is 24, 3 years ago he found out that his gf at the time was pregnant , but they didn't work out and he visited the baby and still saw her often. Long story short one day the ex gf decided that he couldn't visit the daughter, he took her to court, took a paternaity test and found out the baby wasn't his. I recently saw the exes Facebook and her name has the same last name as my BF along with hers at the end. But it also says she's been a relationship with another guy /since 2013 I'm afraid to ask my BF, cuz he's going to think I don't trust him. But in this case I had a right to look through cuz I really love him but I need him to be honest. How should I ask him about this?