For the last 4, 5 years I've been playing my guitar through my laptop by connecting the guitar to my multi-effects processor Zoom G1 and connecting the output from that to my laptop's line-input. I used to get decent guitar sound and could listen to music from my laptop too which I've always found useful for practicing songs. Now a week ago I bought a new laptop which only has one audio jack for the headphones and no line-input so I tried using a ''1 male to 2 female headphone splitter'' but the guitar sound I'm getting isn't good enough and the headphone sound is quite muffled too for some reason.

I looked up different solutions on the net and most articles were suggesting to use either a pre-amp with usb output or an audio interface and it all seemed really confusing. Please tell me what do I need in order to play my guitar by connecting it to a multi-effects processor and connecting that to the laptop and getting a good sound.
Easiest way IMHO is to get a USB interface that includes a DI input and good ASIO drivers. Many can be found used for peanuts. Most of the Midiman/M-Audio USB units are fine, as are the USB Focusrite and Zoom products. If money is no Object, the MOTU and RME units will be awesome, with always up to date drivers and a reluctance on the part of those two companies to leave anything as abandonware. There are many other companies making interfaces on the market that can be hit or miss, there are a few success stories with the TASCAM USB units as well