Hello fellow workers, I've been facing some annoyance the last couple of months. I work in a really big tech company and my team is tiny, we've segregated activities for both me and the other person in the same position as I have to shape focus and productivity, so it's my manager, myself, and a coworker (the one I'm talking about in the title) that holds the same position as I have, but this person is responsible for customer management and I am responsible for sales and partnership management.

In the beginning, it had been working just fine, but now this person wants to know every move I make, wants to join every call I take and even worse, when there are sales trips I need to do, this person also wants to join, even though we have weekly 1:1s to keep stuff synched and usually keep a good stream of communications.

This person is not trying to take me down, nor compete, it's a maniac drive to be working on all my projects and I don't know what to do.

My manager seems to not care or notice, the last trip I took this person requested to go and my manager allowed it. The other day during a team meeting my manager mentioned a call we had with a customer I was managing and my coworker cut him and said "I'm not invited to this call, can you add me?" and my manager simply did it.

Now there's a sales trip coming, and I'm working on this deal alone (there's no commissioning or extras for deals just to clarify) and this person again requested to go along, and there's no need for it.

I don't know what to do anymore, especially because my manager doesn't seem to care at all, even though this behavior is making work less productive because there are two people involved and single-person tasks.

I'm not ambitious, I'm not seeking a promotion, I don't dislike this person at all and I don't care to work as a team but this behavior is annoying me so much, I feel like I'm being disrespected as an individual thinking mind, I even considered quitting this job just to be out of this situation.