Would you?

So my ex and I of 1 year broke up officially about 9 months ago because of some toxic cycles. In that time we both saw other people but recently (a couple months) they contacted ME..we started talking again and things just kind of fell back into place. I noticed they have come a long way since therapy. We basically became official again without the title. Well the other day I called to plan a getaway this weekend with my SO and they were out with a couple friends so the call was short but they didn't sound appreciative or very interested in my plan. Last night we talked and they explained that the night I called they were short because they ended up kind of being interested and flirting with someone they met within the group of friends and they ended up adding eachother on Instagram and exchanging numbers just as "friends" but they clearly told me they were attracted to this other person. They said they know it was wrong and they are sorry, they tell me they are confused and that us coming back together happened so fast and off guard. So I'm at a place now where I feel like if they were willing to give this relationship another serious shot they wouldn't have taken interest in this person they just met. Right? So do I end things or keep trying to make it work because they are just "confused" ?

Just trying to get more input because I do love this person so sometimes that fogs my senses and its not an easy decision. Thanks

CLARIFICATION: "THEY" IS MY EX 🤣