You won't get inclusive texts in Bulgaria, it'll be 11p per text sent (free to receive), 18p per min to receive calls and 35p per min to make calls. Obviously once you come back to the UK your free texts will resume
If you will be calling (Rather than texting) you could get My Europe Extra bolt-on which costs £10 (per month, but cancel when you get back) which makes incoming calls free and outgoing calls about 33% cheaper. So if your partner called you and they get included minutes, it would be essentially free to call you. I guess it depends how much you will be calling as to whether it's worth it.