As GW states, the people to talk to first & foremost are your welfare representatives at CTC upon your return from leave. Depend on the nature of your problem, you can talk to your Corporal, Troop Sergeant, the Padre, the Medical Officer, the Personnel Selection Officer, Naval Personnel Family Services or SSAFA.
Whilst not knowing your specific circumstances (nor asking): To put things into perspective, if ever a Recruit were to doubt whether they wish to continue with RT, it's towards the end of a leave period where all the self-doubts & worries creep in, particularly where family and partners are concerned and or if they have let their fitness lapse. When all's said & done, everyone is different, but you have to give VERY serious consideration to the fact that your being home, may not always be the solution to the problem. (I've lost count of the amount of guys who have left to be with their partner, for example, only to greatly regret leaving a short time later- not that it's suggested this is your situation).
If you submit PVR to leave the Corps, quite often a caveat is attached which means a period must elapse before you may be considered eligible to re-join. Sometimes, it can state you must wait 12 to 24 months before you may re-apply.
If you leave & join the RMR, you will start training (& selection) from the begining. Most RMR units only have one intake per year, so if you miss the intake for the respective year, as an untrained Marine, you could end-up waiting a year before you can start the 12 months plus RMR recruit training.
To sound out the options available if you should leave, you should speak to your local AFCO whilst still on leave so that when you return to CTC you are under no illusion as to what is available.
Good luck, whatever you choose.