Ask yourself, how did she react when you picked up the phone?

To text once a week if you parted on good terms is "ok" but you are suggesting he never answers her and JNS is suggesting that equates to 20 text messages as well as a phone call on Valentines Day. I don't think your SO is hiding anything, he would not give out the home number or tell her never to call, if he was.

I don't think she is over him though.

Perhaps as now you are curious and need to put this to bed, have an Adult discussion with "trust" about it.