If you can't be doing with sitting on an exercise bike now when there is no effort over and above getting off the settee - why would it automatically happen when you've got to get ready, sort out childcare, get your stuff together, get out of the house and travel to a gym?
I love the gym for it being out, air conditioned, peaceful, no need to clean the shower afterwards, because it's a safe environment (unlike the streets), I don't have the space for equipment indoors (or a swimming pool) and it's a time where I can reset my head and enjoy moving and pushing myself, followed by a sauna/steam room, shower and blow drying my hair, applying makeup and coming home via the wanky snacks and fruit in the adjacent Waitrose. It's not to lose weight - it's being done for its own sake. (I did actually shift 7 stone, but that was from changing what I ate and how much I ate, very little of it was due to doing something I enjoyed).
Food and activity are linked, but are of differing levels of relevance.
You want to run again - well, you're going to need to get a lot of weight off first, as shin splints, knee problems, hip pain, Achilles tendonitis and plantar fasciitis are fucking painful. But you also need to get the good feelings from exercise to keep you from eating your feelings down - so less weightbearing and more strength gains and aerobic fitness are needed, along with stabilising your joints, as everything shifts when your weight changes. Which could mean what I did - warm up with 20 mins on the rower, then 20 mins on something else, a slow circuit on weights, then a swim - or yoga, aqua aerobics, just a swim when you're tired or aching, steam room - whatever. But very little high impact work until I was back within the overweight instead of morbidly obese category, and then still far less than other forms of exercise.
The gym can be a treat for you - but you can start treating yourself now with nice food that is lower in calories but higher in nutrition - and the couple of pounds you could lose in a fortnight show that you can do it, with or without the indulgence (a lovely, lovely one, but an indulgence, all the same) of coming home via the gym every couple of days.
You can do it - but it's not dependent upon you going to the gym. It's dependent upon you being kind to yourself and focusing on the food choices you make, not beating yourself up by saying it would have been fixed by now if only...