Both are short bl dramas produced and uploaded to youtube by the same company (strongberry/matchbox). One actor even appears in both shows (but portrays different characters).
While in Beside You only the cat turns human and is the love interest, in CMS both deceased cat and dog return reincarnated to their owner, the dog being the love interest.
Café setting, reluctant falling in love, easy flowing dynamics, humour, some heartbreak. These two shows feel very similar to me and I enjoyed the laidback tone of both.