Why worry? Since when do you have to agree 100% about everything to be friends? And after all, if you managed to become frum while knowing this person, why should it threaten you afterwards? So go on being friends.
As far as sharing Torah, is your friend non-Jewish or Jewish and just not frum? In the first case there might be some wisdom in not discussing religion. In the second case, there’s no reason not to talk about what you are enthusiastic about in Torah so long as you don’t get “preachy” or let it monopolize the conversation.