Painting alone is good. Painting alone every week for two years is how a hobby quietly stops happening. A fixed evening with other people is the most reliable fix for that, and it is the main reason art groups exist.
Here is how to find one and what to expect, plus an honest note about what this is and is not.
First, an honest distinction

Art therapy and a painting group are not the same thing, and it is worth keeping them apart. Art therapy is a clinical discipline, delivered by a trained and credentialed therapist, for people working through something specific. A local art club is a room of people who like painting. Painting as a group activity works on the same principle at a smaller scale.
The second one is genuinely valuable. Regular company, a reason to leave the house, and a few hours a week doing something absorbing with your hands. That is worth having on its own terms, and it does not need to borrow the language of treatment to justify itself. If you need the first thing, look for the first thing.
Where to actually look
The library. Almost always has a noticeboard, and almost nobody checks it. Community centers and church halls are the same.
Your local art supply shop. The staff know who runs what, because those people are their customers. This is the single highest-yield question you can ask, and it takes thirty seconds.
Adult education and community college listings. These run structured classes rather than open groups, which suits some people much better. A term of six weeks is a low-commitment way to find out whether you like the company.
Senior centers, if that applies to you. Often the best-attended and longest-running groups in a town, and frequently free.
Museums and galleries. Many run painting sessions, drop-in workshops or sketching mornings, and they tend to be well organized.
Online listings. Meetup and local Facebook groups will surface things the noticeboards do not. Searching your town name plus painting or art group is usually enough.
The local paper and community magazine. Still where a lot of small clubs advertise, particularly the ones that have been running for thirty years.
Ask one question before you go
Groups vary enormously, and turning up at the wrong kind is the most common bad first experience. Before you commit an evening, ask what actually happens.
A critique group means bringing work and having people talk about it. Useful and not what everyone wants on a Tuesday.
A social painting session means everyone brings their own project and works alongside each other, chatting. No teaching, no assessment.
A class means someone is teaching a technique and you are following.
All three are good. They are not interchangeable, and the answer takes one email to find out.
What you actually get out of it
Not inspiration, mostly. The real benefits are more ordinary and more reliable.
The evening is in the diary. Most abandoned hobbies are not abandoned deliberately, they just lose to everything else. A fixed time defended by other people's expectations survives in a way that good intentions do not.
You see how other people work. Watching someone hold a brush differently, or lay in a background before the subject, teaches you more in five minutes than an hour of searching would.
Someone answers the small question. The one that is too trivial to look up and has been quietly annoying you for a month.
If a group is not your thing
Painting alongside one other person at a kitchen table does most of the same work. Two people, two canvases, no one teaching anyone. It is a good standing arrangement with an adult child, a neighbor or a friend, and it asks nothing of either of you except turning up.
Why numbered canvases work well with company
This is a real observation rather than a sales point. In a room where people have different levels of confidence, a blank canvas creates a visible gap: the people who can draw make something, and the people who cannot sit and feel it.
A numbered canvas removes that entirely. Nobody has to be good, nobody is comparing, and everybody goes home having finished part of something. It is also the format people are most willing to try in front of others, because there is nothing to be exposed at.
If you are setting up a session, the easier designs to start a group on are Summer's Song, Be Still, Away From It All and House Near the Lake. Broad sections, few near-identical colors, and a picture that is recognizable early, which matters when people are watching each other's progress.
The full range is here, and our beginners guide covers what a first one involves.