Why is my bf requesting to follow a girl he used to talk to before me.

why is my bf requesting to follow a girl he was talking to right before we started talking. Partner and I are both 22 and have been dating for 1.5 years. Saw he was following a girl we (and he) has no mutuals with a while back but I didn’t want to ask unnecessary questions so I didn’t ask who she was. Saw about a month ago he got a notification she accepted his request to connect on LinkedIn. Today I asked who she was and he told me he was talking to her right when we started talking but told her he didn’t feel comfortable talking to her anymore as he was now interested in me. He lied and said she requested to follow him but after I told him I saw the notification he said he just didn’t say it was him bc he thought I’d feel a certain way about it. I dislike lying and I feel uncomfortable about the situation but I’m not sure if I’m overthinking it. Why would feel the need to connect with her if he’s got a gf and knows she was into him/ he was into her before. Thank u😅