How do I learn how to trust again?

Me and my boyfriend have been together for 7 years. I just recently found out when I was about 4 months pregnant that he had been lying about working late and had been going out a lot and meeting other woman. He was doing this before we knew we were pregnant, but continued to keep texting relationships with two woman In particular. When I found out he was so closed off and it took for me to get an explanation out of him. I'm 8 months now and now he is always with me and let's me check his phone whenever I want, even let's me keep his gps location on his phone so I know where he's at at all times. But still I have this fear that it won't be like this for long, and that he still might be having desires to go out and meet other people. Is it safe to trust again? How do I do that with keeping my heart safe?