Have you talked to your wife about her libido? About changing meds and talking to a sex therapist maybe? I am sure you did but it doesn’t say in your post.

It feels like cheating because it is probably cheating, depending on how your wife feels about it. Different people have different boundaries, some are ok with open relationships and others are not ok with porn, so depends on where you two fall. Personally for me the line is crossed when you interact with the person and/or pay for it in a sea of free porn.

If you want to stay with your wife and not cheat then that would mean addressing the low libido. There are subreddits for people in dead bedrooms (but read those with caution since people can be salty and vindictive).