Instead of asking, "should I tell him ever?", I would personally be asking, "should I tell him now or risk him finding out later?" Honestly, there are pros and cons either way:

Telling him now is the honest, up-front option. He might be perfectly fine with it, but if you hold off on telling him and he figures it out on his own, he might be mad that you hid it, and start worrying that you've hid more. Telling him now gives you the relief at not carrying around a difficult secret, and gives him reassurance at knowing you were wiling to trust him.

On the other hand, this doesn't affect your relationship, and no one says you have to reveal EVERYTHING about yourself so quickly. You may find in awhile that you've become so comfortable that it'll slip out and he'll shrug and no one cares.

Personally, I'd say that anyone who would be hurt or angry at you revealing this is probably someone you don't want to be with long-term; when the truth eventually comes out to someone like that, it's going to hurt. Someone you loves you will either accept you with open arms, or will at least be willing to try to understand.

If it were ME, I'd first drop a hint or two to see if he's okay with bisexual people, so you have some advanced warning about how he's going to react. Then I'd tell him, focusing on that you're trying to be honest, that it makes no difference to how much you love him and that you just don't want him blindsided if it comes up accidentally some day. You don't even have to tell him you've had relationships with women; you can just say you're bi. If he has further questions, take it from there; if he's great with it but doesn't want to dig up the past, then that's fine to.