don't lie to your boss about being ill.
That is very good advice, why should your company and your colleagues bear the burden/cost of your decision. Here is my take,
1. You know Polish reality.
2. By moving you are being subservient to his needs, not a good foundation for a relationship, in the case of disagreements, you will always remind him that it was you, that moved for him.
3. Is he prepared to support you financially or does he have the financial capability to support you.
4. If you were to have a baby, would it be more beneficial for the baby to be born in the Uk or PL from a financial point of view?
5. How will he assist you in finding a new job in PL?
6. How will you feel taking a large pay cut for him and how will he subsidize your loss of earnings?
You have both worked hard to achieve your professional status, you both have a quality of life and financial independence, that is going to change if one of you quits,if you want to be together, ask him to assist you in seeking out a new job in Poland and make him aware what you are doing for him, is he willing to accept this responsibility. Polish men in their 20's are great talkers, but lack on substance and responsibility, the fact he uses his parent as an emotional tool over you ,highlights this fact.